at zero.

gin decreases very rapidly, and at the margin itself is perhaps In cases of straight margins of great length there is a constant surface motion from the margin toward the centre, most intense at the margin. The average central surface velocity varies on a calm day nearly as the square root of the central depth. The curve representing the mid-channel vertical velocity is approximately a common parabola, whose axis is usually below the surface at a depth depending upon the state of the wind; but the form of the curve is hardly well enough determined to admit of inferring the bottom velocity. The line of maximum velocity is highest at mid-channel, and deeper as we proceed toward the margins.—Professional Papers on Indian Engineering, October, 1875.

GAUSS' THEORY OF CAPILLARITY.

Plateau states that, as is well known, Gauss has deduced formulæ relative to particular phenomena of capillarity, by starting from the principle of virtual velocities. The French scientist Moutier has recently shown that the theory of Gauss properly treated explains certain effects attributed of late years to the tension of liquid surfaces, without any necessity of especially assuming the existence of such tension. He has deduced also a general formula concerning the equilibrium of two liquids in contact with each other and with a solid. This formula contains certain constants relative to the different molecular attractions that obtain in the system; and now Van der Mensbrugghe, of Ghent, demonstrates that these constants themselves have a definite physical signifi cation; that they represent, viz., respectively the tension at the free surface of the two liquids, the tension at their com mon surface, and the tensions at the surfaces of contact between the liquids and the solids.-Bulletin Acad. Royale des Sciences de Belgique, 1875, 366.

LIPPMANN'S EXPERIMENTS ON CAPILLARY ATTRACTION AND HIS ELECTRO-CAPILLARY MOTOR.

The facts in relation to capillary attraction, described by Mr. Lippmann, and of which he has availed himself in the contrivance of what he calls the electro-capillary motor, now exciting so much attention in Europe, are not original with him, but are due to Dr. Draper, who discovered them

more than forty years ago, and made them the subject of a memoir inserted in The Journal of the Franklin Institute of Philadelphia, January, 1836, and again in The London and Edinburgh Philosophical Magazine, March, 1845, in a paper entitled "Is Capillary Attraction an Electrical Phenomenon ?" In these memoirs Mr. Lippmann's facts are set forth, and the explanation of them is given. Dr. Draper formerly wrote a good deal on capillary attraction, regarding it simply as an electric phenomenon. His views on the subject are given in detail in the scientific journals above named, and also in The American Journal of Medical Sci

ences.

ON THE ELASTICITY OF GASES.

One of the most extensive experimental researches of modern times is that now being prosecuted by Mendelejeff on the elasticity of gases, the expenses of which are being defrayed by the Imperial Russian Society of Technology, the first of which is now published in the Russian language. Experiments made by Oersted, Rumford, Natterer, and Cailletet lead one to think that under considerable pressures all gases are compressed less than they should be as indicated. by Mariotte's law. The greater part of the first volume of Mendelejeff's work is of course occupied with preliminary researches necessary to establish the accuracy of his instruments and methods. The volume concludes with a description of the first experiments made by him upon rarefied gases and upon air compressed under from one to three atmospheres. The results that he has obtained in operating upon air, hydrogen, and carbonic acid, under gradually decreasing pressures, lead to the conclusion that the product of the pressure into the volume diminishes with the pressure; the diminution being especially sensible for air, when the pressure becomes very feeble.-6 B, LXXXI., 501.

THE ELASTICITY OF PURIFIED AIR.

Some researches of Mendelejeff and Kirpitschoff show that the product of any volume of air by its pressure, which according to the law of Mariotte should be constant for all pressures, is not so for the air, varying considerably when pressures diminish to so small a quantity as half a milli

the

meter. This product in fact, which for perfect gases is constant, varied rapidly in the case of air. The deviations from the law of Mariotte for rarefied air are contrary to those observed by Regnault for compressed air. In fact, the prod uct increases when the pressure increases, and diminishes when the pressure diminishes. These discordances are far larger than the possible errors of observation.

AIR PUSHED IN FRONT OF A PROJECTILE.

In investigating the various phenomena attending the impact of projectiles, Busch has studied the question as to whether a sphere falling into a fluid drives air before it, or whether the air is simply inclosed by the water as it comes together behind the sphere. The simple apparatus employed by him to study the question consists of a cylindri cal vessel full of water in which a plate is hung having in the centre an opening so large that the sphere falling through the water will be caught by it. His experiments show that in the case of bodies falling with a very small living force, the air above the water has time to be completely pushed aside by the falling projectile. But that if the living force of the body is increased slightly to a certain limit, it no longer becomes possible for the air to be entirely pushed aside; but that a certain amount is pushed by the sphere forward, and the quantity of air so driven on increases with the increase in the living force to precisely the degree required by the measurement of Magnus, upon the quantity of air carried with the projectile into the water. If we increase the resistance of the fluid by taking some more viscid fluid than water, such as glycerine or oil, it is found that a greater living force is required in order to carry the air in front of the projectile into the fluid. Even in the case of a shot penetrating a solid body, such as a thin sheet of India rubber stretched over the opening in the plate, a certain quantity of air is driven through in front of the ball.-Verhandl. Naturhist. Vereins, Bonn, XXXI., 251.

ON THE PROPULSION OF AIR BY A JET OF AIR OR VAPOR.

An interesting and practically valuable series of experiments has been made by Romilly on certain phenomena, which may be described as the dragging or propulsion of

the atmosphere along with a jet of air or vapor. Any such jet, blown from a fine spout, carries with it a certain quantity of the surrounding air. From an extensive series of accurate measurements made by him, he concludes in general that when the jet is received through a tube into a chamber pierced opposite to the receiving spout by an orifice equal and similar to it, the pressure within the chamber is reduced to one half. Second, that whatever distance the orifice of the spout may be, the effect is always greater if the direction of the jet is the same as that of the axis. In all directions inclined to the axis the effect diminishes very rapidly. The experiments made by him have included the use of conical and cylindrical tubes, and open and closed reservoirs.-6 B, LXXX., 189.

EXTENDING THE COMPASS AND INCREASING THE TONE OF STRINGED INSTRUMENTS.

At a recent meeting of the Musical Association of London, Dr. Stone stated that there are three ways in which a string may be made to give very slow vibrations, viz., by increasing its length, its thickness, or its density. He had adopted the third plan by covering a catgut string with heavy copper wire, which proved to be fairly successful. This had been improved upon by re-enforcing the vibrations by means of longitudinal struts or bars, applied to the double bass violin. Four strips of white-wood, curved to an elliptical figure, are passed parallel from end to end, on the inside of the belly of the violin. The result is the removal of what is termed by the musicians "wolf," or inequality and falseness of tone, with a great increase of power throughout the range of the instrument. The same process is equally applicable to small violins, and the bars can be removed at pleasure without damaging the instrument. As an illustration of what may be effected by this system, an instrument whose original cost was 18. 9d. was exhibited to which this improvement had been applied, and its performances called forth great applause.-18 A, XX., 270.

CONDUCTION OF HEAT BY BUILDING MATERIALS.

The coefficient of conduction for heat of various building materials has lately been carefully investigated by Lang,

G

who, in his studies, has endeavored to exclude the influence of radiation, and has made measurements by means of the thermo-electric multiplier. He finds that the stones considered by him are much better conductors of heat when wet than when dry, and that various classes of stones, such as marble, sandstone, granite, etc., have approximately the same co-efficients of conduction, while bricks of all kinds are much worse conductors than the natural stones.

CHANGE OF TEXTURE IN SANDSTONE BY HEAT.

According to Mr. John Young, the sandstone bottoms of iron furnaces assume, from the long-continued action of heat, a distinctly columnar form, the old lines of stratification being obliterated, thus showing that heat, as well as electricity and mechanical force, was an agent in the production of the columnar form of rocks.-15 A, November 20, 676.

ANTIQUITY OF THE BURNING MIRROR.

Buchwalder states, in reference to the burning mirror recently invented by Mouchot, that it was used as long ago as in the days of Numa Pompilius, in whose reign the priests in the temple of Vesta, according to Plutarch, employed a conical reflector, with a solid angle of ninety degrees, as a mirror for concentrating the rays of the sun, thereby producing the heat necessary to light the sacred fires.

OBSERVATIONS UPON RADIOMETERS.

Mr. H. A. Carrington communicates to the Popular Science Review a slight contribution in the way of experiments with radiometers, in which he has arrived at the following conclusions: First. That when the radiometer is receiving light or heat, being at a lower temperature than its surroundings, repulsion of the black disks must ensue, and continue until the temperatures are equalized. Second. When the radiometer is radiating heat, being at a higher temperature than its surroundings, attraction of the black disks, or the apparent repulsion of the white disks, must ensue, and continue until the temperatures are again equalized. Third. No source of light can produce repulsion of the black disks unless it is capable. of raising the temperature of the residual air within the globe. Popular Science Review, April, 1876, 137.